Private branch exchange telephone system



Oct. 23, 1951 w. A. MALTHANER 2,572,740

' PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 17 Sheets-Sheet 1 FIG. STATION ,4 I LINE No.20

STATION 8 LINE No as A TTOR/VEV Oct. 23, 1951 w. A. MALTHANER 2,572;740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 17 Sheets-Sheet 2 4MP: 853N301 En x39 .228 ESE wnozu 2 v :62 #225. 3 dz vats;

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I I 9 Q A TTORNEV Oct. 23, 1951 w. A. MALTHANER PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 l7 Sheets-Sheet 3 lNl EN OR WA. MALTHANER A [TOR/VEV Oct. 23, 1951 w. A. MALTHANER PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM 1'? Sheets-Sheet 4 led May 10, 1948 m/mvrofi WA. ALTHANEH ATTORNEY Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 l7 ShGGtS-ShGGt 5 'lNVE/VTOR W A. MALTHA/VER ATTORNEY Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 1'7 Sheets-Sheet 6 W A. MALTHA/VER A TTOR/VEY Oct. 23, 1951 w. A. MALTHANER' 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 1'7 Sheets-Sheet 7 HOLD MAG/VETS INVENTOR W.-A. MALTHANER ATTORNEY Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 17 Sheets-Sheet a 7/V VE/VTOR By w A. MALTHANER ATTORNEY Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 17 Sheets-Sheet s rnu/wr unnksn cm an r HOIVLER CCTZ //VV EN7'0R -W A. MALTHA/VER BY Oct. 23, 1951 w. A. MALTHANER PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM 17 Sheets-Sheet IO Filed May 10, 1948 QQL M/VE/VTGR 144A ALTHA/VER ATTORNEY 17 Sheet's-Sheet 11 w. A. MAL'THANER PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM uzGzE wiE h Exam Oct. 23, 1951 Filed May 10, 1948 //VVE/VT0R W. A. ALTHA/VER ATTORNEY Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 17 Sheets-Sheet 12 TRUNK CIRCUIT TRUNK CIRCUIT TRUNK CIRCUIT ATTORA/FY Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 l7 Sheets-Sheet 15 0 2:: E E lgs w 3U E INVENTOR ALT HANER ATTORNEY Oct. 23, 1951 w. A. MALTHANER PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Z 1'7 Sheets-Sheet 14 Filed May 10, 1948 //V VE/W'Of? WMALTHA/VER ATTOR/VE Y Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 1'7 Sheet-Sheet 1s /N l/E N TOR 5 WA. MALTHANER Oct. 23, 1951 w. A. MALTHANER 2,572,740

PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM Filed May 10, 1948 17 Sheets-Sheet 16 T0 W/NDINGS OF IN TERMEDIA TE ADYANCING RELAY5 CR T0 TR CONVERTER CIRCUIT lNl/ENTOR WA. MAL m4 IVER BY ATTORNEY Oct. 23, 1951 w. A. MALTHANER PRIVATE BRANCH EXCHANGE TELEPHONE SYSTEM 1'? Sheets-Sheet 17 Filed May 10, 1948 k xvi INVENTOR B WA. MAL THANER Patented Oct. 23, 1951 PRIVATE BRANCH EXCHANGE TELEPHONEV SYSTEM William A. Malthaner, Summit, N. J., assigno'r to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application May 10, 1948, Serial No. 26,028

8 Claims. (01. 179-18) This invention relates to telephone systems and more especially to small-capacity private-branchexchange systems in which the individual stations are equipped with alternating-current generating devices for causing connections to be established therewith.

In my Patent No. 2,408,433 granted to me on October 1, 1946, I disclosed a private-branch-exchange system in which a connection between a station of the private branch exchange and a trunk to a telephone central office may be established by keying, on the alternating-current device at the station, a special code followed by the number of the station. This operation establishes the connection to the central office, from which the line of the calling station may be further extended by connections within the central oflice. Even in the case of a dial central office, however, such extension would have to be effected with the assistance of an operator since the equipment of a dial central ofiice is arranged to be responsive to dial impulses and not to the combinations of frequencies produced by the alternating-current device at the calling station.

It is an object of the present invention to provide means whereby the calling subscriber, having obtained a connection to a dial central office by means of the alternating-current device at his station, can himself control the extension of his connection at the central oifice by means of said device.

A feature of the invention is a means for converting the combination of frequencies produced by the alternating-current device at the calling station into trains of impulses corresponding to the number keyed by the calling subscriber and adapted to operate, in accordance therewith, the usual switching equipment provided at dial central offices.

Another feature of the invention is a novel form of converter for the combinations of frequencies, in which digits represented by said combinations of frequencies are registered by the charging and discharging of capacitors.

Other features of the invention, as well as its mode of operation, will be apparent from the accompanying description, the appended claims,

I and the drawings in which:

' twenty verticals and ten horizontal outlets. To" each of the verticals, a station is connected in accordance with its identifying number, station A being connected to vertical No. 20, station B to vertical No. 39 and other stations being similarlyfl connected to other verticals. Of the ten hori-' zontal outlets, the uppermost six are reserved for three links and the lowermost four are reserved for a maximum of four trunks which may extend either to one central office or to as many as four different central offices. bodiment of the invention, trunk No. 4 extends to a dial central office, indicated in Fig. 12.

Fig. 4, in the left portion thereof, shows a linkallotter circuit, while the rest of the figure, to-

' gether with Fig. 5, shows the call-allotter cir- 1y indicated;

Fig. 14 shows the trunk-markercircuit;

Figs. 15, 16 and 1'7 show the circuits of the converter; and s Fig. 18 shows how the above figures should be placed in relation to one another to completely disclose the invention.

Before describing the invention in detail, at-

tention is called to the fact that this invention is illustrated in connection with the circuits and equipment completely disclosed and described in Patent No. 2,408,433 issued .to me on October 1, 1946, the equipment and circuits shown in said patent having been modified and adapted to carry out the new functions and features of the present invention, including their adaptation for cooperative action with circuits and equipment not shown therein. However, the system shown in said pat: cut is a modification of that disclosed in my Patent No. 2,300,951 issued to me on November Reference may be had to said latter patent for a description of such operationsas are not pertinent to the present invention and not described herein nor in my Patent No. 2,408,433, referred to above, such, for example, as

In the present em-,

the establishment of connections between stations of the private branch exchange.

The construction and operation of the system herein disclosed are, in many respects, similar to those of the system shown in my above-mentioned Patent No. 2,408,433. The link, link allotis connected, through the medium of one of the link circuits and the cross bar switch, to the line i of the calling station and keytone transmitted to said station to advise the subscriber-thereat tokey the wanted number. If the calling subscriber wishes a connection to another station of the privatebranch exchange, he keys the number of said station on the alternating-current device at his station. The alternating-current receiver re= sponds to the frequencies thus produced and, through the translator, operates relays to register the corresponding digits. In this case, th'e 4 is shown in the unoperated position. These three relays control the sequential allotment of an available link to a calling station and the functions of relays CHI and CH2 in the positions shown is to unite the start conductor I to the first available link. In the present embodiment of the invention, it is assumedathat the quantity oftraffic from and between stations of the private branch exchange, including service to the central office, may be adequately handled by three linkswhich I have designated links No. 1, No. 2 and No. 3. Relays CHI, CH2 and CH3 serve to allot eachof said three links in rotation to calling stations. The "operated condition of relays CHI indicatesthatthe link to which it provides access is idle and may be allotted to a calling 7 station. Saidrelay remains locked in the opfirst digit, keyed is, owing to the numbering of the station from 20 to 39, either 2 or 3 and this digit causes the link circuit to operate the cross-bar switch to connect the calling station to the station indicated by the number keyed. If, .on the other hand, the calling subscriber wishes connection to a central ofiice, he keys the special code 4 followed by the number of his own station. The registration of the digit,4

indicates to the link circiiitthat connection to a,

central office trunk is desired but before proceedingto establish such connection, a check is made that the station number keyed is actually that ofthe calling station and, if such is the case, to determine if the calling station is one, entitled to seryice through the central office. Connection is established to the central office trunk, with, the aid of the trunk marker, only if the check shows thatthe required conditions are present.

In accordance with the present invention, however, when the calling station is thusconnected to'the central office trunk, the alternating-cur rent receiver and the translator are not dismissed as. inthe system shown in my above-mentioned patent. Instead, the converter is associatedjwith the trunk and the calling subscriber is advised by-a tone to key the number of'the station with which he desires connection through the. central ofiice. When he keys said number, the alternating-current receiver responds to the combinations of frequencies produced. and, through the translator, registersthe corresponding digitsin the converter. The converter then produces trains of impulses, similar to dial impulses, corresponding to the registered digits whichv are transmitted over the trunk to the central office to operate the switching equipment .thereat to establish the desired connection between the call-. ing andthe called stations. Havingv described the general arrangement and functioning of the invention, I will now describe in detail the operation of the present embodiment of the invention in the establishmentlof a connection from a station of the private branch exchange to a wanted station through a dial centraloflice.

Referring to Fig. 4, thereare. shown therein three relays CHI, CH2 andCH3, which form a Iink-aHofttercircuit. RelaysCHI and CH2 are shown in the operated position, while relay CH3 erated condition until said link is taken into use, the locking circuit extending from battery throu hthe winding of said relay, contacts of key KYLfconduct'or 2; No. 1 contacts of relay-'B of l'inkNo. 1 (Fig. -6')','conductor 3, and No.3 front bracket 5, and No. 6 contacts of relay toground. The operating circuit of relay cnaextends from battery through the winding of said: relay,'contact's of key KY3, conductor 'I-within bracket 8, through contacts of a relay (not shown). in linkNo. 3.similar to relay B-of link No. 1, and conductor 9 within bracket 870'0 the No. 'Bnormal contacts of relay CI-I'I and'the No; 3 front contacts of relay CH3. Both 'of'said latter contacts being open, relay CH3 is not operated;v Start conductor I will be seen to be extended through No. 3 contacts jo'frelay CH2 and No; 1 contacts of relay CHI to link No. 1. In order for acallin'g station to have accessto link No. l; relays CHI and CHZjmust be operated and relay CH3 no't operated. It will be shown later-that, as each link is allotted in rotation, the circuits of relays CHI, CH2 andCH3 are changed to extend start conductor I to the n'ext'idle link in order.

To make a call throu'ghthe central office, the attendant at station .A remove the telephone instrument from its cradle and, upon/receiving fkey tone, keys upon the alternating-current generating device LG of well-known form, the digit '4, indicative of thejtype. of connection desired and, thereafter, the number 20 ofjsta tion A. The removal of the telephone instrument :from its cradle. completes a circuit extending from battery. through the No. '1 normal contacts of hold magnet H020, associated with vertical No- 20, windingof relayLZfl, ring conductor 4|, through the station loop, tip conductor 40, No. 3 normal contacts 'of relay L29; and No. 2 com tactsof cut-off relay COZII'to ground, over which relay L20 operates. Overits No. 3 front contacts, the ground terminal of its circuit is switched from solid groundto ground through the latte hand winding of transformer LBT, to. the right.- hand winding of which isconnected, in the event thatno. link is available, a source of distinctive tone; as described later. Relay L 2]! completes circuits for relayLO'Z aOI the vcall allotter circuit (there being one such relay L020 for each station) assuming relays CHI and CH2 operatedand relay CH3 not operated, and. forrelay SiT of link 'No. i, said link being, under the circumstances assumed, the

fiiferred link for allotment. The circuit of relays L020 and ST extends from battery through the winding of relay ST, conductor l0, No. 1 contacts of relay CHI, No. 3 contacts of relay H2, start conductor I, No. 2 and No. 1 contacts of relay L20, conductor ll, winding of relay L020, and No. 1 contacts of relay E to ground. Relays L020 and ST both operate over this circuit. Relay N then operates over a circuit extending from battery through the winding of said relay, No. 4 contacts of relay MS, No. 1 back contacts of relay M, conductor [2, and No. 1 contacts of relay L020 to ground, completing a circuit from battery through the winding of relay M, No. 1 contacts of relay MS, and No. 2 contacts of relay N to ground, over which relay M operates, opening, at its N0. 1 back contacts, the circuit of relay N, which thereupon releases. The release of relay N opens the operating circuit of relay M but the latter relay remains locked to the ground on conductor l2 under the control of the No. 1 contacts of relay MS and its own No. 2 contacts. When relay MS operates, as described later, relay M releases. This cycle of operations of relays N and M ordinarily performs no useful function but will perform an emergency function described later.

Relay E also operates over a circuit extending from battery through the winding of said relay, conductor l3, the No. 1 back contacts of the individual link relays LKI, LKZ, and LK3 in series, conductor l4, No. 2 contacts of relay L020, and No. 1 contacts of relay El to ground, and locks up through its own No. 1 contacts and No. 1 contacts of relay L020 to ground, completing circuits from battery through the windings of relays El and E2, No. 2 normal contacts of relay MS, No. 2 contacts of relay E, and No. 1 contacts of relay L020 to ground, over which relays El and E2 operate. Relay El, in operating, opens the previously-traced operating circuit of relays L020 and ST but said relays are now locked up over the circuit previously-traced through the winding of relay L020, thence through No. 2 contacts of said relay, conductor l4, No. 1 contacts of relays LK3, LK2, and LKI in series, conductor l3, No. 1 contacts of relay E, and No. 1 contacts of relay L020 to ground. With relays El and E2 thus operated, no operating ground is available for any of the otherrelays, similar to'relay L020, associated with other stations of the private branch exchange. No other station may, therefore, re-

ceive service if a call is originated thereat, while a link is being assigned to station A.

When relay El operates, as described above, it completes a circuit for relay MS from battery through the winding of said relay, No. 14 contacts of relay El, and No. 1 contacts of relay L020 to ground. Relay MS, however, is slow operating and operates only after an interval, its No. 4 contacts then opening the operating circuit of relay N, its No. 2 contacts supplying a holding ground for relays El and E2, and its No. 3 contacts applying the ground on conductor I2 to conductor l5. The ground applied to conductor I5 is used to cause the operation of a link-select magnet, as later described. However, if, through some fault, relay E fails to operate, relay MS cannot operate and ground will not be supplied over conductor l5 to cause the operation of the link select magnet. Under these circumstances, it is desirable to complete the eon-' nection of tation A and emergency means are provided for supplying ground to conductor l5 for that purpose. It will be remembered that when relay L020 operated relay operated, causing the operation of relay M. The operation of relay M caused the release of relay N but relay M remained locked up through its No. 2 contacts and No. 1 contacts of relay L020 to ground. It will be observed that with relay M operated and relay N normal, the ground at No. 1 contacts of relay L020 is connected through No. 1 front contacts of relay M and No. 1 contacts of relay N to conductor l5. Ground is, therefore, supplied to conductor l5 even though relays El and .MS

do not operate. 7

Returning now to relay ST of the allotted link No. 1, when said relay operates, as described above, a circuit is completed from battery through the winding of select magnet SM9, conductor II, No. 2 contacts of relay B, and No. 5 contactsv of relay ST, to the above-traced ground on com.

ductor l5, over which said magnet operates, and conditions the tenth horizontal level of crosspoints of the cross-bar switch for extension of the loop of the calling station A. A circuit is thereby completed from battery through the windings of relays S and SI in parallel, conductor l8, and contacts of magnet SM9, to ground, over which said relays operate and complete a circuit from battery through the windings of cut-ofi relay 0020, conductor l9, No. 3 contacts of relay L020, and No. 3 contacts of relays S and SI to ground. Relay C020 operates over this circuit and closes an.

ductor 50, No. 5 normal contacts of relay MCI, conductor 5|, No. 3 contacts of the closed crosspoint of the cross-bar switch, conductor 52, and

resistors RC and ROI to ground.

The operation described above, of relay ST in link No. l, completes a circuit from battery through the No. 2 normal contacts of relay LS3 and LS2 in series, winding of relay LSl, conductor 53, and No. 4 contacts of relay ST to ground, over which relay LSl in the link-connector cir-f This relay is associated with link cuit operates. No. 1 and, as its operating battery is supplied through normal contacts of relays LS2 and LS3,

associated respectively with links No. 2 and No'. 3, it cannot operate until both of the latter relays are normal. relay LSl connect battery to the winding of said relay to hold it operated independently of relays Relay LCl then operates over a" circuit extending from battery through the wind- LS2 and LS3.

ing of said relay, No. 2 contacts of relay COL, and No. 1 front contacts of relay LSl to ground.

Relay MOI of the trunk-marker connector circuit also operates over a circuit extending from;

battery through the winding of said relay, No. 3 contacts of relay DCT, conductor 54, No. 1 contacts of relay COL, and No. 1 front contacts of relay LSl to ground. Relay LCl connects link No. 1 to the translator circuit and relay MCI connects said link to the trunk-marker circuit.

Relay ST does not release, being now locked up over a circuit ex-. tending from battery through its winding and. N0. 3 contacts, No. 1 contacts of relay T2, con- The No. 2 front contacts of 

